Control circuits



June 9 1942 H. L. BARNEY CONTROL CIRCUITS Filed Dec. 1s, 1940 .K /N VEA/*rop H. L. @ARA/Ey 5V )V27/1 Wella.. ATTORNEY Patented June 9, 1942 UNITED STATES PATENT y OFFICE v y coNraor. cmcmrs nai-old L. Barney, N. J.,- assignor to nen Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 18, 1940, Serial No. 370,600

j 13 Claims. (Cl. 178-44) This invention relates to signal systems' and particularly to gain control circuits for controlling the volume on signal systems.

One object of the invention is to provide gain control circuits for a signal line that shall have a forward acting gain increaser circuit for effecting a fast increase in gain and a-backward act ing gain increase disabler circuit for disabling the fast gain increaser circuit when the signals are abovea predetermined level and for estab-4 lishing a slow gain increaser circuit.

Another object of the invention is to provide a signal system having a variolosser and a nega` the signal line for controlling the gain. The' properly transmitted. In order to prevent overloading the apparatus in the radio transmitter.` the signal currents produced by the weak talker and ,the loud talker are controlled by voice-operi ated V.circuits so that constantv volume is supplied to the radio transmitter.

In the circuits employed to describe tion, a variolosser and a negative feedback ampliiier are included in a signal line. The variolosser in the form of a varistor comprises copper oxide elements disposed in series and in shunt to variolosser is controlled by a forward acting gain increaser circuit, a backward-acting gain dev creaser circuit and a relatively slow backward acting gain increaser circuit. The amplifier is of the negative feedback type and is provided with a resistance element shunted by a cold cathode tube in the negative feedback circuit for increasing the feedback substantially instantaneously when strong inputs are suddenly applied to prelvent any undesirable overloading characteristics.

i A further object of the invention is toprovide f a signal system having a variolosser in the signal eline', a gain increaser circuit'and a gain increase disabler circuit for disabling the gain increaser circuit that shall control the variolosser by a gain phone system it is desirable to have thetelephone currents supplied tothe radio transmitter at constant volume in order to prevent overloading the apparatus in the radio transmitter. In a radio transmitter, it is simpler to effect amplification y and override the noise level encountered in a radio. system when constant volume signals are supplied to the transmitter.

In a telephone` system. voice currents controlled by different types of talkers-are transmitted. In one extreme case may be the very loud talker and in the; other extreme case may be the very weak talker. The volume range including a very loud ftalker and a very weak talker The -gain increaser circuit whichis connected to the signal line before the varistor is of the syllable type. The signal impulses received from the signal' line pass through broadly tuned fre-v quency selective networks and are then amplified.` The amplified signal impulses then pass through another frequency selective network which selects. frequenciesvfof the order of 1000V cycles. 'I'hese signal currents are then applied to a diode-trio'de tube. The signals detected by -the diode results in low frequency impulses which are amplified by the triode and supplied toa syllabic frequency filter. The output from the low frequency syllabic filter has copper oxide elemay be such as to cause overloading of the apparatus in a radio transmitter when the adjustmentsy connected in series and shunt thereto in order to insure that control by the gain increaser circuit is .only eilected on the rising portionv of the syllabic impulses. The syllabic impulses govern a gain increaser relay whichcompletes a circuit for charging a relatively large condenser and a relatively small' condenser. The two control con'densers govern the bias on two control tubes forming one arm of a Wheatstone--bridge. The output vertices from the bridge are connected to a network of varistors in the signal line.

A backward acting gain increase disabler circuit is provided which not only disables the fast v ments are such as to cause the weak talker to be, Il. A backward acting gain decreaser circuit is the invenprovided for governing thevarstor according to both halves of the signal waves. 'I'he gain decreaser circuit charges' the control condensers in an Vopposite direction to the charging effected by the gain increaser circuits. The control condensers govern the control tubes in theWheatstone bridge circuit to control the varistor in the signal line. A cold cathode tube having twoA cathodes and one anodeis included in the gain decreaser circuit. Copper oxide elementsvshunted by resistance elements are connected to the cold cathodes in order to provide a low resistance path in the direction of the wanted current flow.l

lter and retard coil 28 is employed to couple the tube 24 with-the tube 25. A resistance 3| in the cathode circuit is provided for supplying bias to the control grid of the tube 24. A negative feedback circuit is provided from the anode of the tube 25 to the cathode of the tube 24 which comprises a condenser 32 and a resistance element 34 shunted by a cold cathode tube 33.

A full-wave rectiner controlled by the signal wave l supplied to the gain decreaser circuit is connected to the anode of the cold cathode tube to insure that control current passes through the cold cathode tube in one direction only.l Inasr'nuch as the gain decreaser circuit is operated by the full signal waves, it can decrease gain somewhat faster without introducing any more new products in the transmission path due to unbalnces in the varistorf Also since it is full wave control, low frequency transient disturbances accompanying gain decrease action do not cause such wide variations of rate of gain decrease depending on 'the polarity of input to the gain decreaser.' Moreover, full-wave operation of the gain decreaser circuit reduces the spread of output volumes by minimizing the effect of the dissymmetry of speech waves from some carbon transmitters and permits faster gain decrease when required. 'I'he single figure in the accompanying drawing is a diagrammatic 'view'of gain control circuits constructed in accordance with the invention. i

Referring to the drawing a gain control arrangement l is shown connected to a signal line The cold cathode tube 33 breaks down instantaneously when the signals reach a predetermined level to instantaneously increase the feedback. This decreaseof the gain of the amplifier takes place instantaneously and prevents transient disturbances `in the amplifier output. In brief, this feedback arrangement provides a peakchopping action and prevents the signals from causing grid. current flow in the ampliner tube 25.

A gain increaser circuit 35 and a gain decreaser circuit 33 are provided for governing a bridgev circuit 31 to govern the gain by the variolosser 3 so as to maintain substantially constant volume on the output conductors 4 and 5. A gain increaser disabler vcircuit 38 is provided for dishaving input conductors 2 and 3 and output conv ductors 4`and5. A variolosser 5 and a negative feedback amplifier 1 are connected in the signal line for controlling the variable volume received signals to supply constant volume output signals to the output conductors 4 and 5. The input conductors 2 and 3 are connected to the variolosser by -means of a transformer 3 and the variolosser is connected to the amplifier 1 by a transformer 9. The negative feedback amplifier 1 is connected to the output conductors 4 and 5 by means of a hybrid coil I Il. The variolpsser comprises two copper oxide elements and |2 in series with one side of the signal line and respectively shunted by resistance elements I3 and I4. Two copper oxide elements I5 and I3 are connected in series Vwith the other side of the line and are shunted respectively by resistance elements I1 andv I3. Four copper oxide elements |9, 2l, 2| and 22 are provided forv establishing shunt circuits across the signal line to lower the gain. Aresistance element 23 is shunted across the primary winding of the transformer 9 to lower the impedance across the transformer. Direct current circuits are com- -pleted through the .copper oxide elements in series and in shunt with the signal line for varyc a manner to be hereinabling the gain increaser circuit 35 'when the signals are raised to a predetermined level and for establishing a slow gain increaser circuit.

The gain increaser circuit 35 comprises a filter 39, a pentode amplifier tube 40, and a diodetriode tube 4I. The'iilter 39 which comprises two condensers 42, two resistancel elements 43 and the primary of a transformer 44 is connected to the input conductors 2 and 3 ahead of the variolosser 0. The filter 39 is connected to the input circuit of the amplifier tube by the transformer 44. l The output circuitof the'amplifler 40 is connected by a transformer 45 to the diodes of the diode-triode 4|. lA condenser 46 shunted across the primary winding of the transformer 45 provides a broadly -tuned frequency selective network with a peak at approximately 1000 cycles. A battery 41 is provided for supplying anode potential to the tube 40 and a resistance element 43 in the cathode circuit is provided forsupplying grid bias to the tube'40.

The diode-triode 4| comprises a control grid 49, an anode 50, a cathode 5| and auxiliary anodes 52. The circuit through the diode of the diode-triode 4I may be traced from one terminal of the secondary winding of the transformer 45, through the auxiliary anodes 52, cathode 5|, resistance 53 shunted by condenser 54 to the other terminal. of the secondary winding of the transformer 45. Variations in the potential drop across the resistance 53 shunted by the condenser 54 are `impressed on the control grid 49 through a condenser 55. A transformer 55 connects theoutput from the triode of the diodetriode 4| to the operating coil of a gain increaser relay 51. A filter comprisinga condenser 53 and the primary winding of the transformer 55 is provided in the output of the triode of the diodetriode to select impulses of syllabic frequency. Preferably the filter is tuned to approximately 5 cycles. A copper oxide element 59 is connected l connected inshunt to the secondary winding.- of v the transformer 5l in order to restrict operation ofthe gain increaser circuit 35 portions of the signal waves.

The gain increaser relay 51 when operated completes a circuit for charging control condensers Il and I2 in 'a direction to decrease the negative bias on the grids of two control tubes 63 and 94. '.I'he charging clrcuit'c'ompleted yby to initial rising .the gain increaser-relay 51ywhen operated .may

be traced from a ybattery 65 through the armature of a gain increase disabler relay 66, front ment 61, coldcathode tube 68 and ccfmdensery 62 shunted by the resistance elements 69 and18 and condenser 6I to the other terminal of the battery'65.. The .control condenser 6I is'rela- Lively small compared to the sizeof the control condenser 62. The condenser 6I may be of the order of three-tenths of a microfarad whereas the condenser 62 may be four miorofarads.

The plate circuits of control tubes l`63 and 64 form one arm of the Wheatstone bridge circuit 31. The other` arms of the bridge circuit comprise resistance elements 1|, 12 and 13. A grounded battery 14 is connected across two. vertices of the bridge 31 and two conductors 16 and 16 connected to the other bridge vertices a-re joined to `the variolosser 6 for controlling the operation thereof.

Assuming that voice signals on the signal line are of insuicient strength to operate the gain decreaser circuit 36 or the gain increase-disabler circuit 3 8, then the gain increaser circuit 35 will be operated to elect operation of the gain increaser .relay 51 according to the syllabic frequency of the voice currents. Operation of the gain increaser relay 51 completes a circuit forthrough the resistance element 81, resistance ele: ment 88 shunted by condenser 89 and a resistance element 98 to the cathode 82. In like manner, "af similary circuit is completed from the auxiliaryv anode '8| through the ,resistance element 86.` -Thepotential drop across the resistance elenient' 90 serves to impress a bias on the control grid19 when nosignalsare on the signal circuit. The resistance e1eme`n't'88 shunted by the condenser89 serves to impress a bias on the control grid 19 according to the signals on' the signal line. The output circuit .for the triode of the double diode-triode 11 -may beA traced from the grounded*batteryv 6,5 through'the coil ofthe` relay 66, anode 18, cathode 82 and lresistance relement 98 to thefbattery 65r Y When there is no signal input `on the signal line plate current flows through the triode of the double diode-triode 11 sufficiently strong to voperate the relay v|56. When signals are received.,

the negative bias impressed on the control grid 19 mayA be sufficient to release the gain increase disabler relay 66. The sensitivity of the gain impressing a positive charge on the control condensers 6I and 62. control condensers 6| and 62 changes the bias on the grids of the control tubes 63 and 64 to decrease the resistance of the controlv tubes in 6 from the bridge- 31 may be traced from one ter'- minal of the bridge through conductor 15, one secondary winding of transformer 8, copper oxide elements II and I2, respectively, shunted by the resistance elements I3 and I4, primary winding. ,of the transformer 9 and 'conductor 16 to the other terminal of the bridge 31. A second circuit is completed from the bridge 31 through the conductor 15 the other secondary winding of the transformer 8, copper oxide elements |5 and I6, respectively., shunted by the resistance elements I1 and I8, second primary winding of the transformer 9 and the conductor 16 to the other terminal of the bridge 31. The circuits above traced include the yseries copper oxide elementsV II, I2,

The positive charge on the or point of release of the, gain.increase disabler relay 66 is ordinarily Vset four to eight decibels- `greater than that of the gain decreaser circuit 36 to be described later.- In other words, the gain increase disabler circuit 38 is operated'fwhen the signals on the signal circuit have reached ay predetermined strength and prior to the operation of the gain decreaser circuit 36. n

Upon release of the gain increase disabler relay 66 the connection of the battery 65 through the'front contact of the -relay 66 through the front contact .of the gain increaser relay 51 is broken. I No gain increase can take place when at the same time that the gain decreaser relay'.

51 is in released position.

The slow gain increaser circuit is completed when the two relays 5.1 and 66 are in released position and may be traced from the grounded battery 65 through the armature of the relay 66, back contact of the relay 66, resistance elements 88' and 89', back contact and armature of the relay 51, resistance element 61, cold cathode tube 68, condenser 62 shunted by resistance elements- 69 and'il and condenser 6I and ground return to the battery 65. vBy reason of the resistance elements 88 and 89 included in this circuit, it is apparent that thegain increase will be effected I5 and I6 which have their resistance values reduced to increase the .gain on the transmission line. The shunt copper oxide elements I9, 20, 2| and '22 are so poled as to oppose any current ilow'through them by the above-described operation of the bridge 31.

slowly. The gain increase disabler relay 66 has a hang-over time 'of about-two-tenths of a second so that it is held in released position nearly The gain increase disabler circuit 38 comprises A' la double diode-triode`11 having an anode 18, a

control grid llauxiliary anodes 88 and 8| and a cathode 82.

sistance elements 86 and 81. i

The double diode respectively completes circuits through the resistance elements 86 and 81.

The circuit through one-half of the double diode may be traced from the .auxiliary anode 88 7.5

ated as frequently or for as long a period as at high inputA volumes.l Thus, the slow gain increaser action operates more of the time on low input volumes when' the output speech volume is near the propervalue.

. The gain decreaser circuit 36 comprises a 4 three-element coldv cathode tube having an Vanode 0| and two cathodes l2 and 03. and `a full-V completed through the" cold cathodes i2 and 03 by each half-wave signal when of sufficient strength.

The ignition circuit for the com cathin a manner to decrease the gain on the signal 1111. 'l

s relatively fast in operation controls the variolosser ode tube 90' may b traced fromv the cathode 02 through' copper oxideelement |00 shunted by 'resistance element ill, secondary winding over the transformer 09, and copper oxide element |02 shunted byresistance element |0I to the cold |02 are poled in a direction to provide a low "resistance in the direction of the 'wanted current flow and thus speed up gain decrease action .when a' large gain decrease is required.

'Ijhe operating circuit for the tube 90' which is completed through the anode Y9|- of the cold cathode tube 90' may be traced from the anode 0|, through resistance elements 09 and 10 and condensers 0| and l02 in parallel to ground, grounded battery |04. cathode 91 or 98 and anode y'cathode '93. The copper oxide elements |00 and j to. effect a 'quick 'gain increase. The gain `increaser circuit 3 0 ,is disabled by the gain increase disabler circuit 0 0 whenthe signals on the signal circuit have been raised to a predetermined level. The gain increase disabler circuit 30 also establishes a slow gain increaser circuit which operates when the gain increase relay is in released position. The gain decreasr circuitl 20 which is less sensitive than the vgain increase disabler circuit is-operated'by each half signal wave when the signal waves are above a predetermined level. Inthe case of very strong inputs being suddenly -applied to the gain control circuit, itis not desirable to have the gain decreaser to take care of 95 or 90 of the rectiiier SIac'cording to 'whichy .polarity of the signalwa've isimpressed on-the circuit. The two anodes' 95 and' 06 of the rectifier 04 are connected toopposite terminals of the secondary windingv of the transformer 99. Thev rectifier 94 is a full-wave rectifier and insures that current flow through the cold cathode tube 90' can take place only in one direction'. Consequently, the condensersV 0| and 62 cannot be charged in a direction to eect an increase. in.

gain in 'place of a decrease in gain. The copper oxide elements |00 and |02 are.also poledlin a direction to help insure "that the operating circuit of cold cathode tube 90' can only have current flow therethrough in one direction.

Assuming the operation of the gain decreaser circuit 36 is as above described, then a negative charge will be impressed on the control con- 'densers 0| and 02. The control condensers 6| and 62 are of diiferent siz'es and operate in the same manner as the control condensers disclosed in the patent to A. M. Curtis, 2,143,056, June 10, 1939. The negative charge on the condensers 6| and 62 places a bias on the control grids of the negative potential on the conductor 15. When such strong inputs by reason of the ,fact that there is .a delay in the operation of the gain decreaser circuit with the possibility of a few cycles overloading the amplifier tube. In order to take careof strong input signalssuddenly applied to the controlcircuit, -the negative feedback circuit for the amplier 1 is provided with avcold cathode tube which increases the feedback current instantaneously when strong input signals are suddenly applied'to the Sain control circuit.

Modifications-in the circuits and in the ar.'- rangement and location' of parts may be made within the spirit and scope of the invention and such modifications are intended to becovered by the appended. claims.

What is claimed is.: v

1. In gain adjusting circuits, a variolosser for controlling the gain on a signal circuit, means comprising a forward actingfast gain increasing increaser circuit when the signals on the signal the bridge circuit 31 is so operated direct'current Vcircuits are completed through the variolosser similar circuit may be traced from the conductor 10,' through the copper oxide elements 22 and 20 pose any current ow through them at this time. Thus, the `resistance values of the shunted cop- -per oxide elementsL are reduced and no reduction takesy place in the values of theseries copper oxide elements so that the variolosser is -`operated circuit beyond the-variolosser are above a predetermined value, and means controlled by the gain increase disabler circuit for controlling said v variolosser to effect a relativelyslow gain increase on the signal line.

2. In gain control circuits, a gain adjusting device for controlling the gain on a' signal circuit, means comprising a forward acting fast gain increaser circuit for governing said device to raise the gain on the signal circuit at a relatively fast rate, means controlled` by signals on the signal circuit beyond said device for controlling said device to effect a relatively slow gain increase and means comprising 'a backward acting gain increase disabler circuit for preventing control of said device by the fast gain increaser circuit when the signals on the signal circuit beyond said device are above a predetermined level.`

A'to-the conductor 15. The series copper oxide-` elements il, I2, il and I0 are positioned to op- 3. In gain control circuits, a gain adjusting device for controlling the gain on a signal circuit, means comprising a forward acting fast gain increaser circuit for governing saidy device to raise the gain on the 'signal circuit, a backward actslow gain increase whenthe gain increase disabler circuit is in operation and the fast gain increaser circuit is not operated.

4. In gain control-circuits, a gain adjusting delvice for controlling the gain on a signal circuit,

means comprising a forward acting fast gain inincreaser circuit and. means for controlling said device to effect a slow gain increase when the gam for disabling said gain increaser cirlnit when the A increase disabler circuit is in operation and the fast gain increaser circuitis not operated.

5. In gain control circuits, a gain adjusting device for controlling the gain o n a signal circuit, means comprising a forward acting fast gain in'- creasing circuit for governing said device under control of syllabic impulses to raise the gain on the signal circuit, means for insuring control of said device-only on the'rising portion'of a 'syllabic impulse, means comprising a backward acting gain decreaser circuit for controlling said device to decrease the gain onl the signal circuit when the signals on the circuit beyond said device are above a predetermined value, av backward acting gain increase disabler circuit having a greater sensitivity than the gain decreaser circuit for preventing control of said device by the fast gain increaser circuit and means for controlling said device to effect a slow gain increase when the gain increase disabler circuit is in opdecreaser circuit having a three-element cold cathode tube therein' operated by each half of the signal waves when the signals are above a predetermined level for governingsaid device to decrease the gain on the signal circuit and means A comprising a full Wave rectifier in the operating circuit ofsaid tube to prevent reverse current flow through the tube operating circuit.

9. In Igain control circuits, a gain adjusting device for controlling the gain on a signal circuit, means comprising a forward acting gain increascr circuit for l'governing said device to increase the gain on the signal circuit, means comprising a backward acting gain increase disabler circuit signals on the line beyond said device are` raised to a predetermined. level, means domprising a backward acting gain decreaser circuit for governing said device to decrease the gain on the vsignal circuit, a three-element cold cathode tube l in said decreaser circuit having two cold cathodes and an anode, said tube being ignited across said cathodes by each half wave impressed on the gain decreaser circuit when the signals are above a predetermined value, and full wave rectifier means in circuit with the anode of said tube and having the signal waves in the gain decreaser circuit impressed thereon for insuring operation of eration and the fast-gain'increaser circuit is not the gain on the signal circuit.

7. In gain control circuits, a gain adjusting device for controlling the gain on a signal line,

said tube in a direction yto control said device and reduce the gain.

10. In gain control circuits,` a gain adjusting l device for controlling the gain on a signal circuit,

creaser circuit for governing said device to decrease the gain on the signal circuit, a cold cathode tube in said decreaser circuit having two cathodes and an anode, said cathodes having each half wave of signal current on the decreaser circuit impressed thereon to ignite the tube across the cathodes, rectifier elements shunted by resistance elements connected to each of said cathodes in the ignition circuit with the rectifier gain increaser mean's'for controlling saiddevice to raise the gain of the signals on the signal cirf cuit, gain increase disabler means iordisabling said gain increaser means when the signals on the signal line are above a predetermined value,

8. In gain control circuits, a gain adjusting device for controlling the gain on a signalcircuit, j-

gain increaser means for controlling said device to 4raise the gain of the signals on the signal circuit, gain increase ldisabler meansor disabling said gain increaser means when the signals on the signalY circuit are above al predetermined value, means comprising a backward acting gain la varistor followed by a negative feedback am- Y pliier, a resistance element shunted by a gasillled tube connected in series in the negative feedback circuit, said tube' igniting when relatively vstrong input signals are suddenly applied to the amplifier to prevent the peak load on the amplier `from overloading it, means comprising a gain increaser circuit connected tothe trans- -mission line ahead of said varistor for governing.

the varistor to increase the gain, means comprising a.` gain decreaser circuit connectedto the transmission line beyond said ampliier for vgoverningl said varistor to decrease the gain on the transmission line when the signals rise above a predetermined level and means comprising a gain increase disabler circuit connected to the transmission line beyond 'said ampliiier fordisabling said gain increaser circuit, said gain increase disgain decreaser circuit.

6 amer circuit having a higher sensitivity than said 12. In combination, a transmission line having a gain control device therein, a negative feedback ampliiier connected in said line beyond said device, said ampiier having fast acting means in the feedback circuit thereof for limiting the signal peaks, means comprising a gain increaser circuit connected to the transmission line ahead of said device for governing said device to increasethe gain 'on the transmission line, means comprising a gain decreaser circuit connected to the transmission line beyond said amplifier for governing said device to decrease the gain on the transmission line, said gain decreaser circuit being too slow acting to prevent overload of said amplifier by said signal peaks, and means comprising a gain increase disabler circuit connectedy to the transmission line beyond said amplierfor disabling said gain increaser circuit when the signals on the line beyond said amplifier reach a predetermined strength.

combination. a transmissionv line having a gain control device therein, a negative feedback ampiiiler connected in said line beyond said device. a resistance element shunted by a gas-filled tube connected in series in the feedback circuit, said tube igniting when relatively strong input signals are suddenly applied to the amplifier to increase the feedback instantaneously and prevent the peak loads on the ampliiier from overloading it, a forward acting gain increaser circuit for governing said device to increase the gain on the transmission line', means comprising a gain decreaser circuit connected to the transmission line beyond said amplifier and having a time delay for governing said device to decrease the gain on the transmission line and means comprising a backward acting gain increase disabler circuit for disabling said gain increaser circuit when `the signals on the line beyond said 20 ampliiier 'go above a predetermined value.

HAROLD L BARNEY. 

